1. Field of the Invention
The present invention relates to a replacement ankle which is permanently implanted.
2. Description of the Prior Art
Prosthetic devices which are implanted for replacement of joints are well known. Such implants take the place of the body's own joints which fail, such as may be required for patients suffering from rheumatism, degenerative or traumatic arthritis. A number of problems are associated with joint replacement. The joint should function in a manner which simulates the natural joint, providing substantially the same degree of motion. In particular, for ankle replacements, the joint should supply at least the same degree of motion as is required for walking. In addition, the joint should not occupy more space in the body than the natural joint. Problems also arise in connecting the replacement joint to bone and tissue. The joint should also be as easy to implant as possible without the use of surgical cement, so that intricate operations are not required, reducing the chances of complications. The joint must have sufficient strength and durability to withstand the weight and stresses which are applied.
Ankle joints pose additional problems due to the weight supported and the range of motion required for walking. Attachment of the tibia which extends substantially vertically is difficult, as portions of the fibula may also be removed for implants. Matching the pivot point of the joint is critical, as misalignment may lead to difficulty in walking and other motions, which may cause the patient considerable pain. The durability of a replacement joint is also important, as the ankle experiences high stresses during walking, running, and jumping as well as fatigue over time. These stresses may crack or fracture ankle components of replacement joints, which absorb a substantial amount of the pressures during the aforementioned activities.
It can be seen then that a replacement ankle is needed which is inexpensive and easily implantable while providing sufficient range of motion which approaches that of a natural ankle joint. It can also be seen that the utility of such an ankle is increased if the ankle occupies a space comparable to that of the natural ankle and is durable enough to withstand the stresses which are placed upon an ankle joint.